[deanr]

With a little more time on my hands at home these days, I plan on replacing the electrolytic caps in my RE Designs LNPA 150 Amps (made by Dan Banquer).  I wish Dan was still around to ask, but there seem to be some knowledgeable people on here, so don't be shy.

Here are the amps.


An overview, looking down at the two mono amps.


I bought these used so I don't have their complete history but they seem to have the Vishay bulk metal foil resistor upgrade.

My first question - There seems to be a powdery/crystalline substance on the inside floor of both amps.  See pics below.  Is this leakage from the big electrolytics, or is it some kind of old heat grease used on the bridge rectifiers?  Or maybe it is degraded sealant that was intended to prevent corrosion of the aluminum case, or just junk that blew in the vent holes?

[deanr]

These mono amps are supposed to be twins, but the caps on what seems to be the power regulation board don't match up from amp to amp.  It does seem symmetrical between the positive and negative rails in each amp, but the caps in the first amp (pair of 47 uF 100V) are different from the pair in the second amp (100 uF 63V).

When replacing the caps, do I replace them exactly as I find them, or do I make each amp the same?
If I go for uniformity, which amp sets the standard?

[deanr]

I also wonder if one of my channels was out of phase?  The connections to the output terminals seem to have the red and black connected differently as shown in these two photos.





The back panel is not labeled with + or -, and I vaguely recall something about it not mattering because the audio is an AC signal, but shouldn't they at least be consistent?

In the few internal shots I can find on the web, a few more have the red connection on the left/AC power filter side, but a sample size of 4 probably isn't significant. 

[mgalusha]

The upper photo matches the schematic.

These mono amps are supposed to be twins, but the caps on what seems to be the power regulation board don't match up from amp to amp.  It does seem symmetrical between the positive and negative rails in each amp, but the caps in the first amp (pair of 47 uF 100V) are different from the pair in the second amp (100 uF 63V).

When replacing the caps, do I replace them exactly as I find them, or do I make each amp the same?
If I go for uniformity, which amp sets the standard?

[richidoo]

Good catch on the output wires. The output wires are connected to both circuit boards correctly, with red on the right. But they should not cross to the opposite post, they should be geometrically parallel connection, at least according to this pic with colored plastic speaker terminals.
https://ucarecdn.audiogon.com/60f81f18-6a23-4b0b-a32b-29fdb75b3ffb/-/scale_crop/840x630/center/-/quality/lightest/
Technically it doesn't matter as long as speakers get correct polarity. Doesn't look like the wires are long enough to swap them on the posts. Rather than source parts to redo the wiring, I would just keep it as is and mark it on the outside. Either way, make sure your speakers are connected with same polarity from the amp circuit board. The best test for same polarity L/R is to play an old mono recording with strong midrange instrument/voice. The stereo image should be locked dead center. I use Clifford Brown's "I Don't Stand a Ghost of a Chance."    If the image of a mono recording is not centered then just flip one speaker's polarity and hear the change.

The six 47uF caps were intended to be the same. It's unlikely Dan ran out of them during his original build but anything's possible. With the upgraded resistors you found, and the different color 47uFs and 63V 100uFs it seems someone have made some changes since new. I would replace all 12 with new Nichicon Low Leakage (KL?)  47uF 100V from Mouser for both amps. Use good eutectic solder like Cardas, WBT, etc, not 60/40!   

The brown looks like electrolyte. The bad electrolyte from that era reacts with aluminum. The stain is only near the caps. The steel and copper parts in the amp are not corroded from moisture, so I don't think it's rust. The bridge mounting bolts and bypass cap leads on the bridge are not rusted.  These caps could be chinese clones with the notorious bad electrolyte. They leak when hot and spray from the pressure, which explains the large area of residue around the caps. It looks like residue on the edge of the cap heat shrink near the relief hole. Maybe there are small electrolyte spray stains on the wires to caps and bridge? Buy replacements from a reputable supplier, not ebay. https://en.wikipedia.org/wiki/Electrolytic_capacitor#Water_based_electrolytes

Looks like the inside is covered with dust too. You can clean that off with electronics cleaner spray can like CRC. Good luck and thanks for sharing. They are wonderful amps!

[deanr]

Thanks mgalusha and richidoo for the info!

The AC power input has an RFI/EMI filter module.  Do those go bad/get used up over time?

I've noticed a few more differences.  There is what seems to be a fine tuning resistor that is attached between posts that looks different between amps.
 47.5kΩ 1%

 vs.
metal film resistor B(or 8)252FJ


and the some of the trimmers are yellow vs. blue, along with a few other resistor differences.  Could those trimmers still be adjusted after being painted so heavily?

I wonder if someone repaired these.  I recall something about the warranty being void if the amps were used with certain tube pre-amps that were destabilizing and resulting in failure.  Or maybe I'm just seeing a part selection/availability difference over time.

[poseidonsvoice]

Cool rebuild  Subscribed 

Best,
Anand.

[richidoo]

The AC power input has an RFI/EMI filter module.  Do those go bad/get used up over time?

No, just a high pass noise filter.

I've noticed a few more differences.  There is what seems to be a fine tuning resistor that is attached between posts that looks different between amps.
 47.5kΩ 1%
 vs.
metal film resistor B(or 8)252FJ

and the some of the trimmers are yellow vs. blue, along with a few other resistor differences.  Could those trimmers still be adjusted after being painted so heavily?

I wonder if someone repaired these.  I recall something about the warranty being void if the amps were used with certain tube pre-amps that were destabilizing and resulting in failure.  Or maybe I'm just seeing a part selection/availability difference over time.

I think they are both built by Dan at different times. No audio designer worth his salt can ever leave it well enough alone. Are the serial numbers consecutive?

His advice about the tube preamps was to prevent DC being applied to the amp's input. Many tube preamps that lack output relay will make DC until they warm up. Many people can't wait that long. Dan allowed only AudioResearch tube preamps because (apparently) they all had output relay on timer.  He was right in that there was a lot of amateur designed tube junk being sold back in those days. I guess the LPNA-150 does not have input caps?

The paint is designed to lock the trimmer, and notify if it has been changed. The trimmers are probably to set bias current applied to output transistors and should not be touched unless transistors are replaced. Doesn't matter what color they are.

Did you look for the big storage cap replacements?

[deanr]

My amps did not come with serial numbers.  It looks like they were printed on Avery-type labels which can dry up and the crinkle paint prevented full adhesion.  I emailed Dan Banquer back in August of 2006 about the missing labels and he said he would send replacements but that never happened.  (He probably had bigger things going on.)  Mine did have the orange high voltage hazard warning sticker on the back of the case but the adhesive was also toast so I don't know where it is.  The serial numbers would have been a nice clue but Dan seemed to know the seller so I don't think they are counterfeits.

I have some new big Vishay Sprague caps that should arrive today from Arrow (36DY333F075CC2A).  Not easy to find four new 33,000 uF 75 V screw connection caps in those dimensions in stock.  And no way am I going to stick my tongue on them.

[deanr]

Dan also allowed tube equipment from Conrad Johnson, McIntosh, or Audible Illusions (besides AudioResearch).
See his explanation here:
https://web.archive.org/web/20051218081133/http://www.redesignsaudio.com/warrexpl.html
Seems practical and reasonable.

[richidoo]

Fun to read that again, thanks. He was concerned with high frequency, not DC.
I've seen AM radio signal on a scope of the output of a very simple tube preamp with no RF filter.

No, don't stick your tongue on them!! 

[deanr]

I replaced all of the electrolytic caps in both amps.  Here are some pictures of one of them:





Each amp had a fair amount of dried electrolyte that I cleaned up from under the bridge rectifiers, big caps, and boards.  Rubbing alcohol helped remove the mess.  It's not perfect (I thought about taking everything out and polishing the aluminum base) but then again these amps weren't really eye candy to begin with.

I still need to finish the zip tie wire management and adjust some things, but it was a good feeling when I powered them up and they didn't smoke and they worked.  I did have an "oh-no" moment when there was no sound from one of the channels, but then I checked the toggle switches on the side that Dan designed in so you can change cables without any pop/thud/buzzing from the speakers and one of the switches was flipped down from moving it.  If only all fixes were that easy.   

The existing wires were long enough to put both amps in the same phase on the outputs.  I also replaced the RCA inputs because some cables had a hard time making a good connection inside.   Same switchcraft brand, just gold-plated this time.

[deanr]

When I first looked inside this amp, I was struck by the amount of empty space.  I just figured it was to keep the sections cool and isolated.  When I had to remove and replace all those bolts, flat washers, lock washers and nuts, my fingers were very appreciative of the room.

Here is another after pic.


I did run into a small issue when replacing the small 10uf  caps on the signal board.  The holes were too small for my newer caps so I had to carefully expand the hole diameters with a drill.  Traces are still fine after this but I was stumped for a while thinking that I wasn't getting all of the old solder out of the holes.  See the difference in lead diameter here:



A vacuum solder gun made part removal easier.   I found it interesting that solder wick had been used in places to beef up some of the pathways, and a contrast to some of the needle-thin traces.

[richidoo]

Great job Dean! More like a restoration than a repair. Thanks for posting the pics and sharing your project.

How to you like the sound so far? It will change as the caps burn in.

[Russell Dawkins]

I've got to say, this thread makes me miss Dan Banquer.
Not buying one of his amps was a big regret for me; I think they were very 'special' and I would like to have had something to remember him by.
He was real 'old school' and this amp is testimony to 'doing it right, by the book', and good design over fancy componentry.

[poseidonsvoice]

I've got to say, this thread makes me miss Dan Banquer.
Not buying one of his amps was a big regret for me; I think they were very 'special' and I would like to have had something to remember him by.
He was real 'old school' and this amp is testimony to 'doing it right, by the book', and good design over fancy componetry.

+1. I miss also one of his friends in the industry, Mike McCall of Shamrock Audio.

Best,
Anand.

[mgalusha]

Looks great Dean, nice work! One of the few amps I wish I'd kept.

[mgalusha]

Exactly, they are direct coupled.

His advice about the tube preamps was to prevent DC being applied to the amp's input. Many tube preamps that lack output relay will make DC until they warm up. Many people can't wait that long. Dan allowed only AudioResearch tube preamps because (apparently) they all had output relay on timer.  He was right in that there was a lot of amateur designed tube junk being sold back in those days. I guess the LPNA-150 does not have input caps?

[deanr]

How to you like the sound so far? It will change as the caps burn in.

It sounds very nice.  It sounds at least as good as before, so no apparent harm done.  I haven't had much time to critically listen, so part of this is like how your car feels faster after you wash it.   

Most noticeable is the lack of a mild mechanical hum when the amps are powered up.

I measured DC offset with my old Fluke multimeter at the speaker terminals and it is 0.0 mV on both amps.

I'm curious to see if the sound changes as the caps burn in.

The amps seems neutral and linear, without emphasizing any one thing more than another.  One aspect of these amps that I like is that you can turn them up loud but you don't get that sensation of "I need to turn that down," because of how it feels on your ears.  I usually listen at lower volumes and like it there too.

Honestly, my speakers and room set-up probably make it impossible to fully appreciate what these amps can do, but the quality helps.  So my next project will probably by replacing the caps in my 20 year old speaker crossovers.